ELDOR experiments were done using polychromatic irradiation containing more than four frequencies. In this experiment, the pump power was modulated sinusoidally. This was power and not simply amplitude modulation. The pump power modulation is transferred to the observed microwave signal through the ELDOR mechanism and gives the comb of microwave frequencies around the observe signal frequency. Modulation of pump power was used to study the ELDOR mechanism in a single crystal of copper triglycine complex. It was possible to observe ELDOR from copper, nitrogen, and hydrogen hyperfine couplings. The values of the reduction parameter were estimated.